1. Field of the Invention
The present invention relates to a camera with a data recording device and a data recording method therefor. More particularly, the invention relates to a camera with a data recording device and a data recording method in which each bit of digital data is recorded on a photographic film while the film is advanced by one frame.
2. Description of the Related Art
A recording device is known which records on a photographic film exposure control information indicating parameters such as a shutter speed, an aperture value, a use/non-use of a flash, and print information such as trimming data. The recorded information is read during a photofinishing process at a laboratory to control the print exposure or execute trimming of a print. In recording such information, a magnetic recording method or an optical recording method is used.
Digital recording is preferable in order to reduce read/write errors as much as possible. For digital recording, digital data constructed of a plurality of bits is used. Each bit is represented by one of magnetized and non-magnetized areas, or one of exposed and unexposed areas.
Digital data is recorded in association with each frame of a photographic film, for example, at the peripheral area or the lateral side of each frame, while the film is advanced by one frame after photographing. It is required to record each bit to have a predetermined data record length. If a film advance speed is always constant, each bit can be written or read correctly by controlling the read/write period of respective bits, basing upon the constant film advance speed. In this case, the record time of each bit to be written by a magnetic head or light emitting diode, can be controlled in accordance with the constant film advance speed, providing a predetermined record length of each bit. However, in practical situation, the load of a single motor used for the film advance, shutter charge, and the like varies during a one frame film advance. As a result, the film advance speed varies in a complicated manner during a one frame advance, and is also varied for each camera. It is therefore difficult to correctly record each bit by using as a reference the time lapse during a one frame film advance.
To make the record length of each bit uniform, it is necessary to drive a record element such as a magnetic head or a light emitting diode while precisely measuring a film advance speed or length. A conventional data recording device uses a film encoder such as shown in FIG. 15. The film encoder has a roller 72 rotating with the advance of a film 73 and an encoder plate 70 coupled to the roller 72. The encoder plate 70 has a plurality of slits 70a formed at a fine pitch and extending radially. Each slit 70a is photoelectrically detected by a photosensor such as a photo-interrupter. The film advance speed or amount is measured from the number of slits 70a detected during a predetermined time period to control the record time or period.
Use of a film encoder results in an increase of cost. Furthermore, it is necessary to mount it along a film passageway, limiting the mount space and increasing the camera size. It is also difficult to uniformly manage the friction between the roller 72 and film 73. If there is any slip therebetween, the record length of each bit changes. Also, the roller 72 may sometimes scratch the film 73.